Senator Lindsey Graham (R-S.C.) refused to take a COVID-19 test as demanded by his Democratic challenger, Jaime Harrison, forcing organizers of Friday's U.S. Senate debate to change the format at the last minute.

Why it matters: If Graham were to test positive for the virus it could delay confirmation hearings on Trump's Supreme Court nominee Amy Coney Barrett.

• Graham, who is the chairman of the Senate Judiciary Committee, has set an Oct. 12 start date for the hearings.
• Sens. Thom Tillis (R-N.C.) and Mike Lee (R-Utah), who also serve on the committee, recently tested positive for the coronavirus.
• If Graham tested positive, his ability to campaign in person could also be limited, in a race that has become increasingly heated.
• The Cook Political Report on Wednesday updated its forecast for South Carolina's Senate race, moving it from "lean Republican" to "toss up."

Background: Graham and Harrison argued on Twitter Thursday night and Friday after the Democrat said he would not participate in the debate unless the senator took a COVID-19 test.

• Graham accused Harrison of "ducking the debate because the more we know about his radical policies, the less likely he is to win. It's not about medicine, its politics."
• Graham added that the rules of the debate did not require a COVID-19 test, and he cited a note from his doctor that said he did not meet the criteria for needing a COVID-19 test after possible exposure. Last week, Graham said he had tested negative for the coronavirus.
• Harrison questioned why Graham would not take a test when he and the debate moderators agreed to do so.
• Harrison later thanked the event organizers for changing the format.

Of note: The pair faced off behind a plexiglass barrier in their first debate last Saturday.